<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>呼吸灯</title>
    <style>
        div{
            box-sizing: border-box;
        }
       .content{
           width: 360px;
           height: 600px;
           background-color: #333;
           margin: 0 auto;
       }
       .box{
           height: 360px;
           background-color: rosybrown;
           padding: 30px;
       }
       .outer{
           height: 100%;
           border: 5px solid #ccc;
           border-radius: 50%;
           padding: 20px;
       }
       .inner{
           height: 100%;
           border:10px solid #fff;
           border-radius: 50%;
       }
       @keyframes outer{
           25%{
               padding: 20px;
           }
           50%{
               padding: 10px;
           }
           75%{
               padding: 20px;
           }
       }
       @keyframes inner{
           25%{
              padding: 20px;
           }
           50%{
               padding: 30px;
           }
           75%{
               padding: 22px;
           }
           100%{
               padding: 30px;
           }
       }
       .box{

           border: 5px solid;
           animation-name: inner;
           animation-duration: 2s;
           animation-timing-function:inherit;
           animation-iteration-count:infinite
       }
       .outer{
           height: 100%;
           border:5px solid;
           animation-name: outer;
           animation-duration: 2s;
           animation-timing-function:inherit;
           animation-iteration-count:infinite
       }
    </style>
</head>
<body>
    <div class="content">
        <div class="box">
            <div class="outer">
                <div class="inner"></div>
            </div>
        </div>
    </div>
</body>
</html>